Revelations that police may have destroyed key evidence in a gang rape case have prompted a rare personal intervention by Queensland's Opposition Leader, who has demanded an investigation by the corruption watchdog.

Key points:

Deb Frecklington is taking the "extraordinary step" of writing to the CCC on behalf of an alleged gang rape victim

She says she is "appalled" at how much key evidence was destroyed

The victim, 'Eve', says she hopes it will encourage authorities to act on her case

Deb Frecklington put her name alongside the alleged victim in a formal complaint to the Crime and Corruption Commission (CCC).

The Opposition Leader said the "appalling" police handling of the case of "Eve" (not her real name), who reported brutal assaults by at least four men on her 21st birthday, prompted her to take the "extraordinary step" of co-signing the Brisbane woman's formal call for a CCC investigation.

In a scathing letter to CCC chair Alan MacSporran sent yesterday, Ms Frecklington said investigators had "jeopardised the prospects" of the woman seeing her attackers brought to justice and "failed to meet community expectations".

"I am most appalled at the amount of crucial evidence that has been destroyed," Ms Frecklington said.

The revelation came from secret recordings and emails obtained by Eve as she pressed police for a fresh investigation more than two decades later.

"There were things that have been destroyed not just in your case, [but] in cases," a detective said in a covert recording Eve said she made last November.

In the joint letter, Ms Frecklington said lost evidence included "CCTV footage, forensic photographs of injuries, a rape kit, clothing (dress, underpants and bra), a roll of film, entries in the [previous] police database, notes of the investigating officer [and] police statements".

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She said the only evidence left was "one swab taken from the rape kit" and some information in the current police database.

Ms Frecklington said she was also "appalled to learn that only three days were dedicated to the initial investigation and that complainant received no communication, even after the investigating officer identified a new suspect and revealed that further enquiries with the complainant were required".

"The actions of the officer/s involved have jeopardised the prospects of identifying and prosecuting all offenders involved, and consequently, the victim has been denied access to justice," Ms Frecklington said.

She called on the CCC to "investigate the conduct of the officers involved in the matter, as well as to identify the reasons as to why the evidence was destroyed".

She also called for a ban on any police officers "who present a conflict of interest" in any internal investigations of the alleged "misconduct and serious breaches of discipline".

Eve, who was approached by the Opposition about taking her complaint to the CCC and spoke by phone with Ms Frecklington, said she was "really pleased to hear that somebody's taking it seriously because it feels like nobody [in the police] has been taking any of this seriously".

"You go to the police, you expect that they're there to help you, to protect society — not to be the ones that are going to cause you so much distress and actually not even bother," she said.

"So it's good to get some support and to have some stronger language.

"I kind of feel that it needs that instead of [police] just brushing it off as 'just one of those things'."

Eve, who became suicidal after detectives told her the evidence had been destroyed, said she hoped Ms Frecklington's backing would encourage authorities to act on her case.

"To have somebody putting that pressure on, for somebody to actually look at every aspect of the whole case to see where errors have gone on, why it's gone wrong, that that is a good thing, because I want them to learn something from this," she said.

"I want them to never do this again."

Ms Frecklington told the ABC: "She's been through the worst of crimes on her 21st birthday and now horribly, any evidence of that gang rape has been lost".

"I've spoken directly with the victim and I believe there is enough evidence to warrant me adding my weight and demanding of the CCC an external investigation into this matter," she said.

Ms Frecklington admitted this was "an extraordinary step".

She said Eve had been "brave enough to highlight her case to ensure that it never happens to anyone else" and deserved a CCC probe "so we can get to the bottom of what has actually happened".

"We need to ensure that this hasn't happened in any other case, and if it has happened in any other cases, that the victims have been appropriately notified."

Police Commissioner Ian Stewart told the ABC on Thursday he saw the handling of evidence in Eve's case as "a mistake rather than a systemic issue" within the Queensland Police Service.

"Obviously if we're found to have had problems in this space then that would automatically trigger a wider review," he said.

"Yes, we are making inquiries ourselves about all the circumstances relating to this case.

"But I have no problem at all with the CCC coming in and to overview what we've done and, if necessary, to conduct their own inquiries.

"When your [evidence] holdings are so large … the potential for error is possible. Absolutely it's possible, and I hope it doesn't occur and I hope we don't find general evidence of that.

"I haven't seen a huge volume of complaints in this space."

In State Parliament earlier this month, Premier Annastacia Palaszczuk declined to support an Opposition call for an "independent, external investigation of the Queensland police's handling of evidence".

Ms Palaszczuk said the case was under internal review.

In a statement last month, Queensland police "acknowledged there has been difficulties in identifying and locating relevant records and evidence" but denied there was any decision to destroy evidence in breach of their regulations.

A police spokesman also told the ABC that the State Crime Command "continues to investigate the matter".